First, Your question is a great question and is a reasonable one to ask. LingQ is ultimately something that you have to try for yourself to see if it is something you enjoy and feel works for you. With that being said, practically any language learning method will work, the only thing that will really allow you to improve is the time you dedicate to the language.
I personally have seen a huge success with LingQ in at least two languages, that no other method that I have used could even come close to allowing me to progress. I took a year and a half of Mandarin Chinese in college, did mediocre and had terrible sentence structure a low vocabulary and barely was seeing success in the classroom. I, later on, studied various languages as a result of my program of study in my Master’s Program. I even took Classical Chinese for two years in graduate school. Halfway through my graduate program, I started using LingQ. I used it to learn French in conjunction with my school coursework, and in 15 weeks I was reading scholarly articles understanding upwards of 90%.
Before I started French, I was using LingQ to start back with Mandarin. In 4 months of fairly intensive work on my own reading and listening to interesting content (almost entirely on LingQ with a little bit of practice on iTalki), I was having basic conversations with people. I studied on LingQ for about 8 months on Mandarin and was very happy with my progress speed. I ended up stopping on LingQ for a while to focus on my Thesis. I returned to LingQ in mid-January, cleared my program and I am almost back to where I was, and I have to say, LingQ for me is the most useful tool out there for learning most languages. While Hebrew was a pain in the neck as I kept encountering issues with the nikkudot, every other language I have worked with on here I have seen major progress. I am focusing right now on Mandarin, and I wouldn’t call myself fluent yet, but my girlfriend who is Chinese has made comments that my Chinese has drastically improved, both in vocabulary and grammar. I don’t even use LingQ for speaking, but I pay attention when I read, and I notice sentence structures and attempt to use them when I speak. If it were not for this program I would not be able to access material that is constantly keeping me interested in the language, and by extension allowing me to improve. I am not guaranteeing this will be the best system for you, but I recommend anybody who is interested in learning a language, they should at least give LingQ a go. Try it for 6 months in the way that Steve recommends. If you don’t think it is for you then don’t continue. Granted, I don’t only use LingQ, but nobody should just use one method to learn anything, experiment and see what works best for you, but for me, $10 a month is without a doubt worth every penny.
If you are curious as to how I am approaching learning Chinese, then check out my profile, but LingQ is my main resource.
Hope it helps, and I hope you become a LingQ-er. (I do see you have experimented, don’t give up yet).
Best of luck,
-Cody C.